launch_history_manager broken

Please first check if another issue has been opened for your problem

Versions

• OS: Linux
• Gajim version: 161774ed
• GTK version: 3.24.24
• Python-nbxmpp version: 3.0.0.dev1

Steps to reproduce the problem

1. ./launch_history_manager -c /tmp/gajim

Expected behavior

History manager window opens.

Actual behavior

$ ./launch-history-manager.py -c /tmp/gajim
Traceback (most recent call last):
  File "/home/user/gajim/./launch-history-manager.py", line 3, in <module>
    from gajim import history_manager
  File "/home/user/gajim/gajim/history_manager.py", line 89, in <module>
    app.load_css_config()
  File "/home/user/gajim/gajim/common/app.py", line 629, in load_css_config
    from gajim.gui.css_config import CSSConfig
ModuleNotFoundError: No module named 'gajim.gui.css_config'